1. Field of the Invention
The present invention relates to a process for the regeneration of sunflower plants from cell or tissue culture through embryogenesis. More specifically, cells or tissues of sunflower plants are cultured to produce calli. The calli are then cultured to produce embryos which are further cultured to cause germination and plantlet development. The present invention also relates to the sunflower plants and seeds which are produced by this method.
2. Description of the Prior Art
Several methods have been described in the prior art which result in the regeneration of sunflower. All of these methods have involved the use of organogenesis. However, these methods do not appear to be very efficient, and only result in the formation of a few regenerated plants. In organogenesis, plant parts are cultured on a first medium to induce callus formation. The callus can then be transferred to a second medium to induce shoot formation. The shoots are then transferred to a third medium to induce root formation, at which point the regenerated plantlets (plants) can be transferred to soil.
One additional method has been described to produce sunflower plants from an embryo. This method has found use in producing plants from embryos which do not develop in the original plant itself, either because of embryo abortion or seed dormancy resulting from the hybridization of non-compatible species. This method is embryo culture, and has been described by Chandler and Beard in The Sunflower, pages 45-47 (August/September 1980) and Crop Science 23, 1004 (1983). This process involves the rescue of the embryo prior to abortion followed by maturation of the embryo and germination to form the plant.
In this process, young embryos were isolated 3 to 7 days after pollination. These embryos were usually less than 0.1 mm in diameter. The embryos were plated on a solid, growth medium which contained B5 salts, vitamins, amino acids, the auxin .alpha.-naphthalene acetic acid (NAA) at a concentration of 0.05 mg/l, and 12% sucrose. It was found that if 9% sucrose was utilized instead of 12% and 1.0 mg/l indoleacetic acid (IAA) was used instead of NAA, then the young embryos had a tendency to grow as undifferentiated callus instead of embryos. In addition, very young embryos also germinated prematurely on this latter medium.
After 1 to 2 weeks, the enlarged (2-6 mm in diameter) embryos were transferred to a liquid medium for germination of the embryos to plants. During the enlargement period, some of the embryos began root formation and pigment synthesis. The embryos were matured to the cotyledon stage in order to obtain plant formation. The liquid, germination medium contained B5 salts and 1% sucrose. After the embryo generated roots and a shoot, it was transplanted to soil.
The present invention is the first instance of obtaining sunflower plants, i.e., regenerating sunflowers, through the use of an embryogenic callus pathway. Sunflower plants and seeds are produced by this process. The sunflower plants resulting from this process may differ from the starting plant material as a result of somoclonal variation. The pathway is also useful in that it will enable the use of various selection processes to provide further variation. The plants which are produced can then be used in conventional breeding programs.